The myxomycete Physarum flavicomum has a multi-phasic life cycle that is very conducive to the study of growth and differentiation. The plasmodium is a macroscopic single cell containing millions of nuclei. The plasmodial cell cycle lasts about 12 hours and all the nuclei undergo mitotic synchrony, dividing within 30 minutes of each other. These nuclei contain both a cyclic AMP and a cyclic GMP phosphodiesterase. Cytochemical localization of the cyclic AMP enzyme suggest that it is regulated in a cell cycle specific manner. Our long tens goal is to evaluate the role of both nuclear cyclic nucleotide enzymes in the regulation of mitosis in the diploid plasmodium and the haploid myxamoeba stage: and also any role that these enzymes may play during differentiation (sclerotiation, fruiting body formation, and cyst formation). These cells process unique mitotic regulating factors that may be intimately associated with cyclic AMP. A thorough understanding of mitotic regulating factors that might involve 1 cyclic AMP metabolism in these eukaryotic cells may indeed be applicable to higher eukaryotic organisms. Our specific goals are to purify both cyclic AMP and cyclic GMP phosphodiesterase and '.to examine in more detail our preliminary data. This includes heat stability of both enzymes and the ability of each enzyme to bind the opposite cyclic nucleotide. This data has suggested that this may be one protein that hydrolyzes both cyclic nucleotides. Both enzymes will be purified by solubilization from the nucleus and gel filtration, ion exchange and affinity chromatography. These purified enzymes will also be examined for any regulating factors that may be unique to mitosis. These same enzymes from other stages of the life cycle will be studied to determine if they are genetically distinct proteins or are similar proteins that are regulated in a similar manner. Cytochemical localization of these proteins, using electron microscopy, will be done to confirm the presence of these enzymes in other stages of the life cycle.